Conventionally, the orientation of an antenna is adjusted by a rod-like actuator which is illustrated in FIG. 8 of the attached drawings. A motor M rotates a screw S via a reduction gear set G so as to move rod R back and forth. The free end of the rod R is pivotally fixed on the antenna about an axis when the rod extends and/or retracts. A serious disadvantage of the design is that it is difficult to rotate the antenna when the rotated angle is greater than 100 degrees.
To overcome the above-mentioned drawback, a worm and worm gear set is used to replace the rod-like actuator. The design effectively increases the range of rotation. However, as everybody knows, backlash is a phenomenon associated with gearing systems. The problem of backlash increases with the increasing wear and tear of the gear set. A small increment in backlash results in a significant deviation in adjusting the orientation due to the great dimension of an antenna.
In adjusting an antenna, it is necessary to calculate the angle to be rotated with respect to a reference orientation, for example south. It is not possible for the prior art antenna orientation adjusting device to obtain the reference orientation readily. This is also a disadvantage of the prior art.